1. Field of the Invention
The present invention relates to an adjustment method during assembly (manufacture) of a zoom lens system.
2. Description of Related Art
In a zoom lens system, since a state, in which an object image incident on an imaging device is generally out-of-focus (due to focal point shift) when the lens groups are positioned at their standard positions (predetermined at the design stage), occurs due to manufacturing errors such as machining error and/or assembly error, the amount of focal point shift from the short focal length extremity to the long focal length extremity can be optically reduced to a negligible level by carrying out a focus adjustment (zoom adjustment). In a typical focus adjustment method of a zoom lens system, it is necessary for the imaging plane to remain stationary during zooming, and to align this imaging plane with the image-forming plane of the imaging device; and therefore, these adjustments are conventionally carried out by changing the relative positions of at least two lens groups.
For example, in Japanese Unexamined Patent Publication No. H11-30740, a device which adjusts a focal point-shift (caused by machining error and/or assembly error) is disclosed, in which the amount of focal point shift is detected at various focal lengths by moving a lens group which mainly contributes to focus adjustment, the amount of adjustment at each focal length is obtained (via calculation), and correction data is written into a zoom-data table for controlling the positions of each lens group so that it is possible to carry out a focus adjustment by moving the lens groups based on this zoom-data during a photographing operation.
As a mechanical zoom adjustment method, e.g., disclosed in Japanese Unexamined Patent Publication No. 2000-352649, a focal point shift at an intermediate focal length is minimized by changing the standard positions of at least three lens groups during an adjustment at the assembly stage.
In recent years, further miniaturization of digital compact cameras due to further miniaturization of electronic components has progressed, and further miniaturization of the photographing optical system (zoom lens system) is also in demand. From the viewpoint of further miniaturization found in the related art, it is understood that the adjustment method of the related art requires a mechanism for moving each lens group (which mainly contributes to zooming) along the optical axis. However, the structure of such a mechanism is complicated, and the optical design thereof which requires a surplus adjustment has to be further considered among the lens groups. Such an optical design hinders further miniaturization of the zoom lens system.